time: Add new y2038 safe __kernel_timespec

The new struct __kernel_timespec is similar to current
internal kernel struct timespec64 on 64 bit architecture.
The compat structure however is similar to below on little
endian systems (padding and tv_nsec are switched for big
endian systems):

typedef s32            compat_long_t;
typedef s64            compat_kernel_time64_t;

struct compat_kernel_timespec {
       compat_kernel_time64_t  tv_sec;
       compat_long_t           tv_nsec;
       compat_long_t           padding;
};

This allows for both the native and compat representations to
be the same and syscalls using this type as part of their ABI
can have a single entry point to both.

Note that the compat define is not included anywhere in the
kernel explicitly to avoid confusion.

These types will be used by the new syscalls that will be
introduced in the consequent patches.
Most of the new syscalls are just an update to the existing
native ones with this new type. Hence, put this new type under
an ifdef so that the architectures can define CONFIG_64BIT_TIME
when they are ready to handle this switch.

Cc: linux-arch@vger.kernel.org
Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

include/uapi/asm-generic/posix_types.h

@@ -87,6 +87,7 @@ typedef struct {
 typedef __kernel_long_t	__kernel_off_t;
 typedef long long	__kernel_loff_t;
 typedef __kernel_long_t	__kernel_time_t;
+typedef long long __kernel_time64_t;
 typedef __kernel_long_t	__kernel_clock_t;
 typedef int		__kernel_timer_t;
 typedef int		__kernel_clockid_t;